In the context of the present invention, the term “non-precision approach” is understood to be an approach which is not a precision instrument approach, such as for example an ILS (Instrument Landing System) approach. It is known that, in order to use a precision instrument approach, ground stations are used, which are located at the edge of the runway, and at least one special radio receiver installed in the aircraft, which provides horizontal and vertical guidance before and during the landing by showing the pilot the lateral deviation with respect to an approach line and the vertical deviation with respect to a descent plan. Such a precision instrument approach provides great and effective assistance in landing (by lateral guidance and vertical guidance), in particular in poor visibility (fog, etc) or when there is no visibility.
A non-precision approach, such as considered in the present invention, therefore exists when the preceding items of information are totally or partially unavailable, such that a normal precision approach cannot be used.
In order to use a non-precision approach, it is necessary to determine a virtual path, corresponding to the theoretical path that the aircraft must follow during this approach. The guidance of the aircraft then consists in trying to cancel the possible deviations between the actual position of the aircraft and the position that it would have if it were on this virtual path.
The accuracy of the latter is of course essential, at least in the immediate proximity of the runway, for the success of the landing in total safety.